U.S. patent number 6,578,435 [Application Number 09/447,984] was granted by the patent office on 2003-06-17 for chemically inert flow control with non-contaminating body.
This patent grant is currently assigned to NT International, Inc.. Invention is credited to Bob Chinnock, Jerry Cucci, Chuck Gould, Jane Lanctot, Tom Peterson, Dan Wink.
United States Patent |
6,578,435 |
Gould , et al. |
June 17, 2003 |
Chemically inert flow control with non-contaminating body
Abstract
A fluid control module that may be connected in-line within a
chemically corrosive or ultra pure fluid flow circuit that delivers
fluids in either a liquid or gaseous state. The fluid control
module of the present invention may be utilized to control the
flow, pressure or volume of fluid flowing through the fluid flow
circuit and is capable of automatically adjusting or "calibrating"
the module to compensate for changes in atmospheric pressure or
drift in the pressure sensors of the fluid control module. The
fluid control module also includes a rapid or macro adjustment of
the control valve to reach the desired flow rate at a quicker
pace.
Inventors: |
Gould; Chuck (Minneapolis,
MN), Lanctot; Jane (Minneapolis, MN), Cucci; Jerry
(Minneapolis, MN), Peterson; Tom (Chanhassen, MN), Wink;
Dan (Maple Grove, MN), Chinnock; Bob (Victoria, MN) |
Assignee: |
NT International, Inc.
(Fridley, MN)
|
Family
ID: |
23778546 |
Appl.
No.: |
09/447,984 |
Filed: |
November 23, 1999 |
Current U.S.
Class: |
73/861.52; 137/2;
137/487 |
Current CPC
Class: |
G01F
1/36 (20130101); G01F 1/38 (20130101); G05D
7/0635 (20130101); Y10T 137/776 (20150401); Y10T
137/0324 (20150401) |
Current International
Class: |
G01F
1/34 (20060101); G01F 25/00 (20060101); G01F
1/37 (20060101); G05D 16/20 (20060101); G05D
7/06 (20060101); G01F 001/37 (); E03B 001/00 () |
Field of
Search: |
;73/861.52,861.47
;137/2,7,8,9,486,487,487.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
0990885 |
|
Sep 1999 |
|
EP |
|
5-33044 |
|
Oct 1991 |
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JP |
|
07072029 |
|
Jun 1994 |
|
JP |
|
06201063 |
|
Jul 1994 |
|
JP |
|
2552093 |
|
Nov 1996 |
|
JP |
|
3-97639 |
|
Sep 2000 |
|
JP |
|
Other References
Published Article: A Code High-vacuum Seal without Gaskets, Lloyd
Manebo, University of California, Lawrence Radiation Laboratory,
Livermore, California, Contract No. W-7405-eng-48, Sep. 1, 1962.
.
Published Article: Development of a High Temperature Capacitive
Pressure Transducer, R. L. Egger, NASA Lewis Center, Contract NAS
3-19556. Oct. 1977. .
Published Article: Quartz Capsule Pressure Transducer for the
Automotive Industry, C.Y. Lee and J.L. Pfeifer, SAE Technical Paper
Series, No. 810374. Feb. 1981. .
Published Article: Small Sensitive pressure transducer for use at
low temperatures, W. Griffioen and G. Frossati, Rev. Sci. Instrum,
56 (6), Jun. 1985, pp. 1236-1238. .
Article: A Balanced Resonant Pressure Sensor, Erik Stemme and Goran
Stemme, Sensors and Actuators A, 21-A23 336-341. Feb. 1990. .
Article: Diversity and Feasibility of direct bonding: A survey of a
dedicated optical technology, Applied Optics, vol. 33, No. 7, (Mar.
1, 1994) 1154-1169..
|
Primary Examiner: Patel; Harshad
Attorney, Agent or Firm: Patterson, Thuente, Skaar &
Christensen, P.A.
Claims
What is claimed is:
1. A chemically inert fluid control module adapted to be connected
with a fluid flow circuit, the fluid flow conduit conveying a
process fluid, said module comprising: a chemically inert fluid
conduit; an adjustable control valve coupled to the conduit,
wherein a portion of the control valve that is exposed to process
fluid is chemically inert; at least a first pressure sensor coupled
to the conduit, wherein a portion of the first pressure sensor that
is exposed to process fluid is chemically inert; a constriction
disposed within said conduit, said constriction having a reduced
cross-sectional area thereby restricting flow of fluid within the
conduit; and a chemically inert housing enclosing said control
valve and said first pressure sensor; wherein the control valve is
controllable to set a selected fluid pressure, fluid flow rate, or
fluid volume as desired responsive to pressure sensed by the first
pressure sensor, wherein the chemically inert material of the
conduit, first pressure sensor and housing includes a
non-contaminating polymer.
2. The fluid control module as recited in claim 1, further
including a second pressure sensor coupled to the conduit, wherein
said constriction is positioned between said first and second
pressure sensor.
3. The fluid control module as recited in claim 2, further
including a controller coupled to said control valve and to said
first and second pressure sensors.
4. The fluid control module as recited in claim 3, wherein said
controller re-zeros said first and second pressure sensors when
flow within said flow conduit stops.
5. The fluid control module as recited in claim 3, wherein said
controller determines the pressure within the fluid conduit.
6. The fluid control module as recited in claim 3, wherein said
controller determines the flow rate within the fluid conduit.
7. The fluid control module as recited in claim 6, wherein said
controller adjusts a signal to compensate for a pressure
differential present when the rate of flow is zero.
8. The fluid control module as recited in claim 1, wherein said
constriction is positioned between said first pressure sensor and
an area of constant pressure.
9. The fluid control module as recited in claim 1, wherein said
control valve includes a chemically inert diaphragm.
10. The fluid control module as recited in claim 9, wherein said
control valve further includes a second chemically inert diaphragm
and a vent formed between the chemically inert diaphragms.
11. The fluid control module as recited in claim 1, wherein said
control valve is driven by an actuator for actuating the valve
between an open and closed position.
12. The fluid control module as recited in claim 1, wherein said
control valve is pneumatically actuated.
13. The fluid control module as recited in claim 1, further
including a controller coupled to said control valve and said
pressure sensor.
14. The fluid control module as recited in claim 13, wherein the
controller produces a signal proportional to the fluid flow rate
within the fluid conduit.
15. The fluid control module as recited in claim 13, wherein the
controller produces a signal proportional to the fluid pressure
within the fluid conduit.
16. The fluid control module as recited in claim 13, wherein said
controller compensates for changes in atmospheric pressure.
17. The fluid control module as recited in claim 13, wherein said
controller includes a means for macro and micro adjustment of the
control valve.
18. The fluid control module as recited in claim 13, wherein said
controller adjusts a signal to compensate for a pressure
differential present when a rate of flow is zero.
19. The fluid control module as recited in claim 1, wherein the
portion of the pressure sensor exposed to fluid is comprised of
sapphire.
20. The fluid control module as recited in claim 1, wherein the
chemically inert material includes a fluoropolymer.
21. The fluid control module as recited in claim 20, wherein the
fluoropolymer includes polytetrafluoroethylene (PTFE).
22. The fluid control module as recited in claim 1, wherein a
chemically inert material includes a fluorocarbon polymer.
23. The fluid control module as recited in claim 1, wherein the
constriction is formed integrally with said conduit.
24. The fluid control module as recited in claim 1, wherein said
control valve includes a double chemically inert diaphragm with a
vent formed therebetween.
25. The fluid control module as recited claim 1, wherein the
constriction is positioned downstream from the first sensor and the
first sensor is positioned downstream from the control valve.
26. A chemically inert fluid control module adapted to be connected
within a fluid flow circuit, said module comprising: a chemically
inert housing having a fluid conduit extending through said
housing, said conduit having a constriction disposed within said
conduit, said constriction having a reduced cross-sectional area
thereby restricting flow within the conduit; means for sensing a
pressure within the fluid conduit, wherein a portion of the means
for sensing exposed to fluid is chemically inert; and means for
controlling a size of an opening in a valve positioned within said
fluid flow conduit, the valve being controllable to set a selected
fluid pressure, fluid flow rate, or fluid volume as desired
responsive to pressure sensed by the means for sensing, wherein a
portion of the means for controlling exposed to fluid is chemically
inert, said means for sensing and said means for controlling being
contained integrally within said housing, wherein the chemically
inert material of the housing, pressure sensing means and
controlling means includes a non-contaminating polymer.
27. The fluid control module as recited in claim 26, wherein said
means for sensing includes first and second pressure sensors
coupled to the conduit, the conduit constriction being positioned
between said first and second pressure sensors.
28. The fluid control module as recited in claim 27, further
including a controller coupled to said means for controlling and
said means for sensing.
29. The fluid control module as recited in claim 28, wherein said
controller resets said means for sensing when flow within said flow
conduit stops.
30. The fluid control module as recited in claim 28, wherein said
controller determines the pressure within the fluid conduit.
31. The fluid control module as recited in claim 28, wherein said
controller determines the flow rate within the fluid conduit.
32. The fluid control module as recited in claim 28, wherein said
controller adjusts a signal to compensate for a pressure
differential when the rate of flow is zero.
33. The fluid control module as recited in claim 28, wherein said
controller includes a means for macro and micro adjustment of the
means for controlling.
34. The fluid control module as recited in claim 26, wherein said
valve includes a double chemically inert diaphragm.
35. The fluid control module as recited in claim 34, wherein said
valve further includes a vent formed between the diaphragms of the
double chemically inert diaphragm.
36. The fluid control module as recited in claim 26, wherein said
valve includes a chemically inert diaphragm.
37. The fluid control module as recited in claim 26, wherein said
means for controlling is driven by a means for actuating the valve
between an open and closed position.
38. The fluid control module as recited in claim 26, wherein said
means for controlling flow is driven pneumatically.
39. The fluid control module as recited in claim 26, further
including a controller coupled to said means for controlling and
said means for sensing.
40. The fluid control module as recited in claim 39, wherein said
controller determines the pressure within the fluid conduit.
41. The fluid control module as recited in claim 39, wherein said
controller determines the flow rate within the fluid conduit.
42. The fluid control module as recited in claim 39, wherein said
controller compensates for changes in atmospheric pressure.
43. The fluid control module as recited in claim 26, wherein the
portion of the means for sensing exposed to fluid is comprised of
sapphire.
44. The fluid control module as recited in claim 26, wherein the
chemically inert material includes a non-contaminating polymer
comprised of polytetrafluoroethylene (PTFE).
45. A chemically inert fluid control module adapted to be connected
with a fluid flow circuit, said module comprising: a chemically
inert housing having a fluid conduit extending through said
housing; a control valve coupled to the conduit, the control valve
being controllable to set a selected fluid pressure, fluid flow
rate, or fluid volume as desired responsive to a sensed pressure in
the fluid conduit, wherein a portion of the valve exposed to fluid
is chemically inert; a first pressure sensor coupled to the conduit
and to the control valve, wherein a portion of the first pressure
sensor exposed to fluid is chemically inert; a second pressure
sensor coupled to the conduit and to the control valve, wherein a
portion of the second pressure sensor exposed to fluid is
chemically inert; and a constriction disposed within said conduit
between said first and second pressure sensors, said constriction
having a reduced cross-sectional area thereby restricting flow
within the conduit, the first and second pressure sensors sensing
pressures in the conduit on respective sides of the constriction,
wherein the chemically inert material of the housing, conduit
control valve, first and second pressure sensor and constriction
includes a non-contaminating polymer.
46. The fluid control module as recited in claim 45, wherein said
control valve includes a double chemically inert diaphragm.
47. The fluid control module as recited in claim 45, wherein said
control valve includes a chemically inert diaphragm.
48. The fluid control module as recited in claim 45, wherein said
control valve is driven by a means for actuating the valve between
an open and closed position.
49. The fluid control module as recited in claim 45, wherein said
control valve is driven pneumatically.
50. The fluid control module as recited in claim 45, further
including a controller coupled to said control valve and said first
and second pressure sensors.
51. The fluid control module as recited in claim 41, wherein said
controller determines a pressure within the fluid conduit 41,
wherein said controller determines a flow rate within the fluid
conduit.
52. The fluid control module as recited in claim 50, wherein said
controller determines the flow rate within the fluid conduit.
53. The fluid control module as recited in claim 50, wherein said
controller compensates for changes in atmospheric pressure.
54. The fluid control module as recited in claim 50, wherein said
controller resets said first and second pressure sensors when flow
within said flow conduit stops.
55. The fluid control module as recited in claim 50, wherein said
controller adjusts a signal to compensate for a pressure
differential present when the rate of flow is zero.
56. The fluid control module as recited in claim 45, wherein the
portion of the first and second pressure sensors exposed to fluid
is comprised of sapphire.
57. The fluid control module as recited in claim 45, wherein the
chemically inert material includes a non-contaminating polymer
comprised of polytetrafluoroethylene (PTFE).
58. A chemically inert fluid control module adapted to be connected
with a fluid flow circuit, the fluid flow conduit conveying a
process fluid, said module comprising: a chemically inert fluid
conduit; an adjustable control valve coupled to the conduit,
wherein a portion of the control valve that is exposed to process
fluid is chemically inert; at least a first pressure sensor coupled
to the conduit, wherein a portion of the first pressure sensor that
is exposed to process fluid is chemically inert; a constriction
disposed within said conduit, said constriction having a reduced
cross-sectional area thereby restricting flow of fluid within the
conduit; and a chemically inert housing enclosing said control
valve and said first pressure sensor;
wherein the control valve is controllable to set a selected fluid
pressure, fluid flow rate, or fluid volume as desired responsive to
pressure sensed by the first pressure sensor.
59. The fluid control module as recited in claim 58, wherein the
chemically inert material includes a ceramic material.
60. The fluid control module as recited in claim 59, further
comprising a second pressure sensor coupled to the conduit, wherein
said constriction is positioned between said first and second
pressure sensors.
61. The fluid control module as recited in claim 60, wherein the
chemically inert material includes a non-contaminating polymer
comprised of polytetrafluoroethylene (PTFE).
62. The fluid control module as recited in claim 58, wherein the
constriction is formed integrally with said conduit.
63. The fluid control module as recited in claim 58, wherein said
control valve includes a double chemically inert diaphragm with a
vent formed therebetween.
64. The fluid control module as recited in claim 58, wherein the
constriction is positioned downstream from the first sensor and the
first sensor is positioned downstream from the control valve.
65. The fluid control module as recited in claim 58, wherein the
chemically inert material includes a non-metal material.
66. A chemically inert fluid control module adapted to be connected
with a fluid flow circuit, the fluid flow conduit conveying a
process fluid, said module comprising: a chemically inert fluid
conduit; an adjustable control valve coupled to the conduit,
wherein a portion of the control valve that is exposed to process
fluid is chemically inert; at least a first sensor coupled to the
conduit, wherein a portion of the first sensor that is exposed to
process fluid is chemically inert; and a chemically inert housing
enclosing said control valve and said first sensor, wherein the
chemically inert material of the conduit, control valve, first
sensor and housing includes a non-contaminating polymer.
67. The fluid control module as recited in claim 66, wherein the
polymer includes a fluoropolymer comprising polytetrafluoroethylene
(PTFE).
68. The fluid control module as recited in claim 66, wherein the
control valve further includes two chemically inert diaphragms with
a vent formed therebetween.
69. The fluid control module as recited in claim 66, wherein a
constriction is positioned within said conduit downstream from the
first sensor and the first sensor is positioned downstream from the
control valve.
70. The fluid control module as recited in claim 69, further
comprising a second sensor coupled to the conduit and positioned
downstream from the constriction.
71. The fluid control module as recited in claim 66, further
comprising a constriction disposed within said conduit, said
constriction having a reduced cross-sectional area thereby
restricting flow of fluid within the conduit.
Description
FIELD OF THE INVENTION
This invention relates generally to fluid controls and more
particularly relates to a chemically inert fluid control module
that may be connected in-line within a chemically corrosive fluid
flow circuit that delivers fluids in either a liquid or gaseous
state. The fluid control module of the present invention may be
utilized to control the flow, pressure or volume of fluid flowing
through the fluid flow circuit and is capable of automatically
adjusting or "calibrating" the module to compensate for changes in
atmospheric pressure or drift in the pressure sensors of the fluid
control module.
BACKGROUND OF THE INVENTION
Caustic fluids are frequently used during ultra pure processing of
sensitive materials. The susceptibility to contamination of the
sensitive materials during the manufacturing process is a
significant problem faced by manufacturers. Various manufacturing
systems have been designed to reduce the contamination of the
sensitive materials by foreign particles and vapors generated
during the manufacturing process. The processing of the sensitive
materials often involves direct contact with caustic fluids. Hence,
it is critical that the caustic fluids are delivered to the
processing site in an uncontaminated state and without foreign
particulate. Various components of the processing equipment are
commonly designed to reduce the amount of particulate generated and
to isolate the processing chemicals from contaminating
influences.
The processing equipment typically includes liquid transporting
systems that carry the caustic chemicals from supply tanks through
pumping and regulating stations and through the processing
equipment itself. The liquid chemical transport systems, which
includes pipes, tubing, monitoring devices, sensing devices,
valves, fittings and related devices, are frequently made of
plastics resistant to the deteriorating effects of the caustic
chemicals. Metals, which are conventionally used in such monitoring
devices, cannot reliably stand up to the corrosive environment for
long periods of time. Hence, the monitoring and sensing devices
must incorporate substitute materials or remain isolated from the
caustic fluids.
The processing equipment commonly used in semiconductor
manufacturing has one or more monitoring, valving, and sensing
devices. These devices are typically connected in a closed loop
feedback relationship and are used in monitoring and controlling
the equipment. These monitoring and sensing devices must also be
designed to eliminate any contamination that might be
introduced.
In order to control the flow or pressure within the liquid
transporting system, the transporting equipment may utilize
information obtained from each of the monitoring, valving and
sensing devices. The accuracy of the information obtained from each
of the devices may be affected by thermal changes within the
system. Further, the inaccuracy of one device may compound the
inaccuracy of one of the other devices that depends upon
information from the one device. Further, frequent independent
calibration may be required to maintain the accuracy of each
individual device, however, independent calibration of the devices
may prove difficult and time consuming.
Hence, there is a need for a non-contaminating fluid control module
which may be positioned in-line within a fluid flow circuit
carrying corrosive materials, wherein the module is capable of
determining the rate of flow based upon a pressure differential
measurement taken in the fluid flow circuit, and wherein the
determination of the rate of flow is not adversely affected by
thermal changes within the fluid flow circuit, and wherein
calibration of the pressure sensors of the fluid control module
does not require ancillary or independent calibration of the valve.
A need also exists for a fluid control module that avoids the
introduction of particulate, unwanted ions, or vapors into the flow
circuit. The present invention meets these and other needs that
will become apparent from a review of the description of the
present invention.
SUMMARY OF THE INVENTION
The present invention provides for a fluid control module that may
be coupled in-line to a fluid flow circuit that transports
corrosive fluids, where the fluid control module may determine
pressure and flow rates and control the pressure, flow or volume
within the fluid flow circuit. The rate of flow may be determined
from a differential pressure measurement taken within the flow
circuit. The fluid control module compensates for changes of
temperature within the fluid flow circuit and provides a zeroing
feature which compensates for differences in pressure when the
fluid is at rest and negates the affects of the valve upon the
system. In the preferred embodiment, the components of the fluid
control module include a housing having a chemically inert fluid
conduit, an adjustable control valve coupled to the conduit,
pressure sensors coupled to the conduit, and a constriction
disposed within the conduit having a reduced cross-sectional area
to thereby restrict flow of fluid within the conduit and allow for
reliable flow measurement. The chemically inert housing encloses
the control valve and the pressure sensors.
When two pressure sensors are provided, the constriction is
positioned between the two pressure sensors within the fluid flow
conduit. As described in greater detail below, the fluid control
module of the present invention having two pressure sensors
provides for bi-directional fluid flow and may be coupled in line
to adjacent ancillary equipment. In an alternate preferred
embodiment, the fluid control module includes only one pressure
sensor, wherein the constriction within the fluid conduit must be
positioned downstream of the pressure sensor and valve. Also, the
fluid control module having a single pressure sensor must be spaced
apart a predetermined distance from ancillary equipment connected
in line to the fluid flow circuit.
The drive or actuation of the control valve may be driven either
mechanically, electrically or pneumatically by a driver having a
known suitable construction and the valving components within the
control valve may take on any of several suitable known
configurations, including without limitation a poppet, diaphragm,
redundant diaphragm, weir valve and/or pinch valve, wherein the
components in direct contact with the fluid of the fluid flow
circuit are constructed from chemically inert materials.
A controller or integrated circuit may be electrically coupled to
the control valve and pressure sensor or sensors. The controller
may produce a signal proportional to a fluid flow rate within the
fluid conduit and/or a signal proportional to a pressure within the
fluid conduit. The controller may control the pressure, rate of
flow, or volume such that a desired set point is maintained. The
set point may be defined by the user or automatically determined by
the controller (for example, during a macro adjustment of the
control valve). Further, the controller may adjust the fluid flow
rate signal or pressure signal dependant upon changes in
atmospheric or fluid pressure. Also, the controller may include a
means for macro and micro adjustment of the control valve in
response to changes in internal fluid or atmospheric pressure and
may re-zero the pressure sensors when flow within the fluid flow
circuit stops.
The housing that encloses the control valve and pressure sensors
includes a bore extending therethrough, which forms a passage or
conduit through which fluids flow, when the housing is connected
in-line in a fluid flow circuit. Aligned and sealably connected to
the opposed open ends of the bore are pressure fittings. The
pressure fittings are constructed from a chemically inert material
and are readily available and known to those skilled in the
art.
In an embodiment of the present invention the housing has two
pressure transducer receiving cavities extending from an external
surface thereof, wherein each such cavity communicates
independently with the bore. An isolation member may prevent the
fluid flow from contacting the pressure transducer receiving
cavities. The isolation members may be molded integral with the
housing or may be removable. The bore tapers to a constricting
region located between the two cavities. The restricted region
results in a pressure drop within the bore across points adjacent
the two cavities. This change in pressure may be detected by
pressure sensor transducers placed within each of the two cavities.
The rate of flow may be determined from the drop in pressure. The
determination of the rate of flow using the two pressure sensors is
described below in greater detail.
A hybrid or fully integrated electronic circuit disposed in the
housing is operatively coupled to both pressure sensor transducers
and the control valve. The electronic circuit develops a signal
that is a measure of the rate of flow within the flow circuit from
information sensed by the pressure sensors. Further, the electronic
circuit may develop a signal corresponding to one or the other of
the downstream or upstream static pressures within the fluid flow
circuit, such that the orientation of the flow meter within the
flow circuit is interchangeable and the direction of flow may be
indicated by comparing the sensed pressure from each pressure
sensor. When sensing the static pressures of gases flowing through
the flow circuit, a correction may be made to the sensed pressures
to correct for non-linearity and flow rates as a result of gas
density and compressibility differences and effects.
This electronic circuit may also be used in combination with
temperature sensitive components to adjust the pressure measurement
associated with each cavity based upon temperature changes within
the flow circuit. Further, the electronic circuit or controller may
allow for zeroing of the pressure sensors and valve control. The
electronic circuit is coupled by electrical leads to an electrical
connector and power may be transmitted to the electronic circuit
through the electrical leads connected to an external power supply.
Further, an analog output such as a standard 4-20 milliamps signal,
voltage output, or digital protocol proportional to the calculated
rate of flow may be transmitted through additional electrical leads
to a display or external controller.
The isolation membrane, pressure sensor, sealing members, spacer
ring and hold down ring may be contained within each cavity of the
housing. These components and variations thereof are described in
greater detail in U.S. Pat. Nos. 5,869,766 and 5,852,244 which are
assigned to the same assigns as the present application, the entire
disclosure of which is incorporated herein by reference. In a
further alternate embodiment, inert sapphire pressure transducers
are positioned within respective cavities and in direct contact
with the fluid flow, thereby eliminating the isolation
membrane.
In use, the fluid control module is coupled in line to a fluid flow
circuit. The pressure sensors may be pre-calibrated or the sensors
may be calibrated at the time of interconnection with the fluid
flow circuit. When calibrating the pressure sensors, the valve may
be actuated between an open and closed position. When the pressure
sensors indicate that flow has stopped, the output required to
actuate the valve may be noted and thereby define an approximation
of the closed position of the valve. Various set points may be
identified to identify the valve position at various pressures,
temperatures and flow rates. The calibration of a single pressure
sensor will be described below in greater detail.
Once the flow meter is calibrated, the user may then select whether
to control pressure, flow or volume within the fluid flow circuit.
If pressure is controlled, the pressure and/or rate of flow is
monitored and the valve is accordingly adjusted until a desired set
point is reached. If flow is controlled, the pressure and/or flow
is monitored and the valve is actuated until the desired set point
is reached. The volume of fluid flowing through the fluid conduit
may be controlled by monitoring both the pressure and rate of flow
and accordingly adjusting the control valve to produce the desired
volume of fluid flow. For example, the user may determine that 2
milliliters of fluid is desired. The valve is opened and the
pressure and flow rates are monitored, such that it may be
determined when 2 milliliters of fluid have passed through the
module, wherein the control valve then closes terminating the fluid
flow.
When flow is controlled, the controller may store in memory the
output of the control valve driver required to obtain a certain
flow. In this manner, when the user selects a desired flow, the
controller sets the output of the driver approximately equal to an
output that previously resulted in the desired flow rate (the macro
adjust). Then controller may then manipulate or "fine tune" the
control valve to precisely obtain the desired flow rate (the micro
adjust). When the flow through the module is terminated by closing
the control valve, the controller may then automatically adjust or
re-zero the pressure sensors such that the difference between the
measured pressures of the two pressure sensors is zero. In this
manner, inaccuracy due to thermal changes and sensor drift is
avoided. In an alternate preferred embodiment, a second valve is
provided, wherein the second valve is a dedicated open/close valve.
The output of the controller or electronic circuit may be delivered
to an external controller or display.
The advantages of the present invention will become readily
apparent to those skilled in the art from a review of the following
detailed description of the preferred embodiment especially when
considered in conjunction with the claims and accompanying drawings
in which like numerals in the several views refer to corresponding
parts.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial sectional side elevational view of the fluid
control module of the present invention;
FIG. 2 is a partial sectional side elevational view of an alternate
embodiment of the fluid control module of the present
invention;
FIG. 3 is a partial sectional side elevational view of an alternate
embodiment of the fluid control module of the present invention
having a pneumatic actuated valve;
FIG. 4 is a partial sectional side elevational view of an alternate
embodiment of the fluid control module of the present
invention;
FIG. 5 is a partial sectional side elevational view of an alternate
embodiment of the fluid control module of the present
invention;
FIG. 6 is a partial sectional side elevational view of an alternate
embodiment of the fluid control module of the present
invention;
FIG. 7 is a partial sectional side elevational view of an alternate
embodiment of the fluid control module of the present invention
having a single pressure sensor;
FIG. 8 is a partial sectional side elevational view of an alternate
embodiment of the fluid control module of the present invention
having a single pressure sensor; and
FIG. 9 is a flowchart showing a sequence the controller may
implement to control the fluid control module of the present
invention.
DETAILED DESCRIPTION
The present invention represents broadly applicable improvements to
chemically inert fluid controls. The embodiments detailed herein
are intended to be taken as representative or exemplary of those in
which the improvements of the invention may be incorporated and are
not intended to be limiting. Referring first to FIG. 1 the fluid
control module is generally identified by numeral 10. The fluid
control module 10 generally includes a rectangular housing
consisting of a housing body 12 and housing cover 14, mounting
plate 16, pressure inlet/outlet fittings 18, pressure transducers
20 and control valve 22. The housing body 12 and housing cover 14
are preferably manufactured from a chemically-inert,
non-contaminating polymer such as polytetrafluoroethylene (PTFE).
The cover 14 has bores 24 extending through it for mounting the
cover 14 to the housing 12 with appropriate screws. A gasket of
known suitable construction is preferably positioned between the
cover and housing to allow the cover 14 to be sealed to the housing
12. Without any limitation intended, a gasket or seal manufactured
from a multi-layer fabric, sold under the GOR-TEX trademark by W.L.
Gore & Assoc., Inc., allows venting of an internal area of the
housing 12 for true atmospheric pressure reference, while
restricting the flow of liquids into the internal area of the
housing 12.
A longitudinal bore 28 extends through the housing 12 forming a
conduit. Thus, when the fluid control module 10 is connected
in-line with a fluid flow circuit, via pressure fittings 18, the
bore 28 serves as the fluid flow passage within the fluid flow
circuit. The orientation of the fluid control module 10, within the
fluid flow circuit, may be reversed without affecting its
effectiveness. A constricting area 30 is formed in the bore 28
between the two pressure sensors 20 to create a pressure drop as
the fluid flow traverses the constricting area or orifice 30.
In the preferred embodiment, cylindrical cavities 32 extend from an
outer surface of the housing 12 to the bore 28. Those skilled in
the art will appreciate that cavities 32 may each extend into the
housing from different sidewalls of the housing. The two cavities
32 are separated a predetermined distance by dividing wall 34. Near
the region within the housing where each cavities 32 and bore 28
intersect, an annular lip 36 is formed. Each lip 36 surrounds and
further defines the opening to each cavity 32 from the bore 28. A
thin flexible polymer disk or isolation membrane 38 is positioned
on the lip 36 of each cavity 32. Without limitation, the membrane
is preferably constructed to have a thickness in a range between
0.001 and 0.040 inches. Preferably, the flexible membrane 38 is
manufactured from fluorocarbon polymers. One such
tetrafluoroethylene fluorocarbon polymer is sold under the TEFLON
trademark by E. I. duPont Nemours. Alternatively, the isolation
member 38 may be molded integral with the housing 12 to form a thin
wall separating the cavity 32 and bore 28.
Each pressure transducer 20 is held in place within their
respective cavities 32 by spacer ring 48 and externally threaded
hold down ring 50. The isolation membranes 38 and transducers 20
are sealed within the housing 12 by chemically inert o-ring seals
52. A redundant seal is created by the positioning of o-ring 54.
The seals 52 and 54 are readily available and of known construction
to those skilled in the art.
A drain or conduit 40 may be formed extending through the housing
12 into each cavity 32 between the redundant seals 52 and 54,
thereby draining the area between the redundant seals. In this
manner, the drain acts as a drainage, passageway or outlet, in the
event that fluids leak past seal 52 from the fluid flow circuit. A
sensor 42 may be positioned within the drain 40 and electrically
connected (by leads not shown) to integrated circuit or controller
46. Those skilled in the art will appreciate that a conductive
sensor, capacitive sensor or non-electric fiber optic sensor may
equally be used to sense the presence of fluids in the drain 40.
When fluid leaks past the first seal, the fluid activates the
sensor 42, thereby transmitting a signal to the electric circuit 46
which subsequently sets off a leak indicator. The redundant sealing
arrangement helps prevent exposure of the pressure transducer 20
and controller 46 from the potential damaging affects of the
caustic fluids. The redundant seal also further isolates the fluid
flow, thereby reducing the potential contamination of the
fluids.
Each pressure sensor 20 may be of a capacitance type or
piezoresistive type known to those skilled in the art. The base of
each pressure sensor is in direct contact with the membrane 38 and
may be either in pressure contact with or bonded to the membrane by
an adhesive, thermal welding or by other known suitable fixation.
In an alternate embodiment, an alumina ceramic pressure sensor may
be used, wherein the alumina ceramic pressure sensor comprises a
thin, generally compliant ceramic sheet having an insulating spacer
ring sandwiched between a thicker, non-compliant ceramic sheet. The
first thin ceramic sheet or diaphragm is approximately 0.005 to
0.050 inches in thickness with a typical thickness of 0.020 inches.
The thicker ceramic sheet has a thickness range between 0.100 to
0.400 inches. The spacer ring may be constructed of a suitable
material such as a glass, polymer or alternatively the ceramic
sheets may be brazed together. The opposed faces of ceramic disks
are metalized by metals such as gold, nickel or chrome to create
plates of a capacitor. A similar capacitive pressure transducer is
described by Bell et al. in U.S. Pat. 4,177,496 (the '496 patent).
Other capacitive pressure transducers similar to that described in
the '496 patent are available and known in the art. It is
contemplated that the flexible membrane 38 could be eliminated if
the pressure sensor used is of the sapphire capacitive pressure
transducer type. A sapphire capacitive or sapphire piezoresistive
transducer type is inert, and is resistant to wear when subjected
to caustic fluids. Having a sapphire sensor in direct communication
with the fluid flow may further enhance the pressure measurements
of each transducer.
The controller 46 may be in any of several forms including a
dedicated state device or a microprocessor with code, and may
include Read Only Memory (ROM) for storing programs to be executed
by the controller and Random Access Memory (RAM) for storing
operands used in carrying out the computations by the controller.
The controller 46 is electrically coupled to a power supply and
manipulates the electrical circuitry for sensing pressure and
controlling the actuation of the control valve, wherein flow,
pressure and/or volume may be controlled.
The controller 46 is used to convert the pressure readings from the
two pressure transducers 42 and 44 to an analog or digital
representation of flow or, alternatively, a pressure reading of the
downstream pressure transducer. The raw analog signal from the
upstream transducer is supplied to an input terminal and, likewise,
the raw analog transducer output signal from the downstream
transducer is supplied to an input terminal. The controller 46
computes the instantaneous pressure differences being picked up by
the upstream and downstream transducers and performs any necessary
zeroing adjustments and scaling.
It is known that, in steady-state flow, the flow rate is the same
at any point. The flow rate (I) may be expressed as I.sub.m
=.rho.vA. Where .rho. represents the density of the fluid, v
represents the velocity of the fluid, and A represents the area
through which the fluid travels. Using the continuity equation
A.sub.1 v.sub.1 =A.sub.2 v.sub.2, the rate of flow within the fluid
control module 10 may be found equal to a constant multiplied by
P.sub.1 -P.sub.2. The controller 46 thus computes the pressure and
rate of flow from the data received from the two pressure sensors.
Those skilled in the art will recognize that with laminar flow, the
rate of flow approximates more closely a constant multiplied by
P.sub.1 -P.sub.2. Hence, a low flow limit could be built into the
system, such that if the "Reynolds number" is below a certain
threshold, the flow meter identifies the flow rate as zero. The
controller 46 may then convert the computed rate of flow into a
digital signal or an analog signal falling in the range of from 4
mA to 20 mA for use by existing control systems.
As fluid flows through the flow circuit, the pressure adjacent each
of the two cavities is detected by the controller 46, whereby the
rate of flow may be calculated from the two detected pressures. The
gauge pressure or absolute pressure may equally be used. Those
skilled in the art will recognize that the flow rate may be
calibrated so that minimum desired output values are associated
with minimum pressure and maximum desired output pressures are
associated with maximum pressure. For example, a pressure sensor
intended to measure 0 to 100 psig (pounds per square inch gauge)
can be calibrated to read 4 mA (milliamps) at 0 psig and 20 mA at
100 psig.
The conduit 28 interconnects with the control valve 22, wherein a
valve seat 60 is formed within the fluid conduit. A double
diaphragm 62 is actuated fore and aft, wherein when the diaphragm
is actuated into engagement with the valve seat 60, fluid flow past
the valve seat is terminated. Alternatively, a single diaphragm may
be utilized to control the flow of fluid past the valve seat 60
(see FIG. 2). Those skilled in the art will appreciate that the
double diaphragm 62 is unaffected by changes in atmospheric
pressure. The driver 66 shown in FIG. 1 used to actuate the
diaphragm 62 is of the electric motor type. Those skilled in the
art will appreciate that the actuation of the valve between the
open and closed position may be accomplished with any of several
mechanical electrical or pneumatic drivers of known suitable
construction. Further, without limitation, the mechanism for
opening and closing flow may comprise for example, a diaphragm,
poppet, weir valve, or pinch valve with the diaphragm and valve
seat being preferred.
FIG. 3 illustrates an alternate embodiment of the driver 66 being
of the pneumatic type. A piston 68 is sealed within a sealed
chamber 70, wherein the mechanical force of a compression spring 72
forces the piston 68 in a downward or first direction and a
pressurized air line 74 increases the pressure on the lower end 76
of the piston to force the piston 68 upward thereby compressing the
spring 72. In this manner, the air pressure within the chamber 70
may be increased or decreased a controlled amount to actuate the
piston 68 and thus the diaphragm 64 attached to the piston 68
between an open and closed position. The lower end of the diaphragm
64 may include a conical member 78 extending therefrom which may
enhance the sealing between the valve seat 60 and the diaphragm 64
(see FIG. 4). Alternatively, a valve stem 80 extending from the
piston 68 may extend through the chamber wall 82 through a bore 82
having a seal 84 to seal the air chamber 70 and provide for fore
and aft motion of the valve stem 80 within the bore 82 (see FIG.
5). The lower end 86 of the valve stem 80 seals directly with the
valve seat 60 when in the closed position. The lower end 86 may be
tapered to further enhance the sealing between the valve stem 80
and the valve seat 60 when in the closed position (see FIG. 6).
Referring to FIGS. 7 and 8 alternate embodiments of the fluid
control module 10 are shown having a single pressure sensor for
determining flow rates within the fluid flow conduit. The control
valve 22 shown in FIG. 7 is pneumatically driven as described above
in greater detail. The control valve 22 shown in FIG. 8 is actuated
by the motor 66 as described above in greater detail. When
determining flow rates with the fluid control module of the type
shown in FIGS. 7 and 8, the orifice 30 must be downstream of the
pressure sensor 20 and control valve 22 and the output end 90 of
the fluid control module 10 must be connected to a conduit, tubing,
void, or other pathway wherein the pressure therein is at
atmospheric pressure (a known constant). In this manner the flow
rate may be determined as described above, wherein the pressure P
on the downstream side of the orifice is a constant. Additionally,
a tubing of known length and diameter may be coupled to the output
end 90 of the fluid control module 10, whereby the pressure
difference between the pressure at the output end 90 and the
pressure within the tubing is constant. In use, the tubing may be
filled with fluid and then the control valve 22 may be shut. The
pressure sensor is then calibrated to indicate zero pressure. When
the control valve is opened, then the pressure sensor will indicate
the change in pressure.
Having described the constructional features of the present
invention the mode of use in conjunction with FIG. 9 will next be
described. The controller 46 either automatically or when prompted
by the user calibrates the pressure sensors 20 and control valve 22
(see block 100). During the calibration process, the controller
creates and stores in memory values corresponding to valve
position, flow rate and internal and external pressure for
predetermined set points. Once the valve position, flow and
pressure are known for desired set points, the controller may
automatically set the valve position based on determined flow
pressure or demand by the external process. Alternatively, the user
may select a desired set point and the controller adjusts the valve
position based on measured pressure and flow rates (see block 102).
The controller then determines whether it is desired to control
pressure (see decision block 104). If pressure is to be controlled,
the controller monitors the pressure and/or flow rate and adjusts
the valve to keep the pressure at a controlled amount (see block
106). If it is not desired to control pressure, the controller then
determines whether it is desired to control flow (see decision
block 108). If flow is to be controlled, the controller monitors
pressure and/or flow and adjusts the valve to keep the flow rate at
a controlled amount (see block 110).
The control may include a macro and micro adjust of the control
valve, wherein the controller stores values associated with flow
rate, pressure, temperature and valve position for the set points.
When the flow, for example, is controlled the controller adjusts
the valve to roughly approximate the valve position for prior
measured pressure temperature and valve position for the desired
flow (the macro adjust). Thus, the flow rate may be approximated
rather quickly and then the control may make minor adjustments to
the valve position to obtain an even more precise control of flow
(see block 112). If volume is to be controlled (see decision block
114) then the flow rate and pressure are monitored and the valve is
opened for a time sufficient to allow the controlled volume of
fluid to pass past the control valve 22 (see block 116). If neither
the pressure, flow or volume is to be controlled then the
controller waits to receive input (see loop 118 and block 102).
During fluid processing, the controller 46 may automatically
re-zero or calibrate the pressure sensors when the control valve 22
is closed (see block 120). Alternatively, a second dedicated valve
may be provided which is operable in either an open or closed
position. The controller may be programmed to re-zero the pressure
sensors when the second dedicated valve is in the closed position.
During processing, the pressure within the flow conduit may undergo
significant changes, thereby requiring changes in the valve
position to keep the flow rate, for example, constant (see block
122). The controller 46 waits to receive the next input (see loop
124 and block 102). Thus, the control module of the present
invention eliminates the additional components and disadvantages of
interconnecting individual pressure sensors and individual control
valves.
This invention has been described herein in considerable detail in
order to comply with the patent statutes and to provide those
skilled in the art with the information needed to apply the novel
principles and to construct and use such specialized components as
are required. However, it is to be understood that the invention
can be carried out by specifically different equipment and devices,
and that various modifications, both as to the equipment and
operating procedures, can be accomplished without departing from
the scope of the invention itself.
* * * * *